This invention relates generally to power control systems and more particular to a method and apparatus for determining the source voltage supplied to a resistive heating element.
Starting in approximately 1984, low cost personal laser printers became available. All dry electrophotographic copiers and printers develop an image utilizing a dry toner. The typical toner is composed of styrene acrylic resin, a pigment-typically carbon black, and a charge control dye to endow the toner with the desired tribocharging properties for developing a latent electrostatic image. Styrene acrylic resin is a thermo-plastic which can be melted and fused to the desired medium, typically paper.
The typical fusing system in an electrophotographic printer or copier is composed of two heated platen rollers which, when print media with a developed image pass between them, melt the toner and through pressure physically fuse the molten thermal plastic to the medium. Heating is usually accomplished by placing a high power tungsten filament quartz lamp inside the hollow platen roller.
The heating element in the fusing system provides enough heat to properly fuse the toner to the medium. The fusing system must compensate for different media types, changes in ambient environmental temperature, as well as dramatic changes in relative humidity. Relative humidity variations greatly affect the fusing system due to the hygroscopic properties of both the print media and the toner itself. When relative humidity is high both the media and toner absorb a large percentage of their dry mass in water that is essentially boiled off during the fusing process thus decreasing the amount of energy available for melting the toner for adhesion to the media. Thus, the fusing system must accommodate a large variety of environmental conditions as well as differing media demands.
Presently, most printer and copier fusing systems and their temperature control systems are not designed to compensate for differing media types or changes in relative humidity. The typical fusing system is designed with a heating element capable of providing enough heat to deal with all foreseen media and relative humidity conditions with little or no concern to the resulting poor power quality that results. Some relatively new printers do utilize relative humidity sensors to adjust print quality and optical sensors to differentiate between paper and overhead transparencies. These additional sensors, which are being added to the printing mechanisms in order to improve image quality, can also be utilized by the fuser control systems to improve temperature regulation as well as improve the power quality of the overall printing system.
There are numerous reasons to intelligently control a electrophotographic printer or copier fusing system in a much more aggressive manner. For example, intelligent control can result in a universal fuser that can be shipped to any commercial market worldwide regardless of the power system. A universal fuser has the attractive benefit of requiring a single part for both manufacture and field service replacement. The manufacturer is relieved of the burden of manufacturing 110 VAC and 220 VAC printers. The need to stock two types of service parts is eliminated, and product distribution centers now have one product that can be shipped to any country in the world without any reconfiguration requirements. There are reduced logistical burdens for sales, distribution and manufacture scheduling. As can be expected there is a large financial advantage to be gained by producing only a single version of a product for worldwide consumption.
For a dry electrophotographic fusing system to operate worldwide it must be able to operate satisfactorily on AC power systems providing from 90 Vrms to 240 Vrms at frequencies of 50 Hz to 60 Hz. The fusing system must heat up from ambient room temperature to operating temperature as quickly as possible while exhibiting extremely low flicker as its power consumption level changes. The fusing system, when combined with the balance of the electrophotographic printer power electronics, must meet International Electrical Commission (IEC) regulations IEC 555-2 and IEC 555-3 for current harmonics and flicker. The printer or copier must pass Federal Communications Commission (FCC) class B regulations for power line conducted emissions and radiated emissions. In addition, the printer must pass CISPR B requirements for power line conducted emissions and radiated emissions. Finally, the printer must not suffer from excessive acoustic multi-tone or single tone emissions in the human auditory range in the office environment. The fusing system must be capable of switching into a power down or power off mode for energy savings as suggested by the EPA Energy Star Program. The absolute cost of any additional electronics is limited to no more than the cost benefit of not stocking multiple 110 VAC and 220 VAC models.
U.S. Pat. No. 5,483,149 to Barrett (herein referred to as Barrett) shows that a universal fuser may be obtained through the use of a modified integral half cycle (IHC) power controller but without solving the flicker problem. The method taught by Barrett has been shown to suffer some flicker problems as well as placing current sub-harmonics on the AC power system. Currently no regulation exists regarding AC current sub-harmonic content. It is sufficient to note that AC current sub-harmonics are unwanted on the power grid and that AC current sub-harmonics in the 4 Hz to 20 Hz range significantly contributes to the flicker level exhibited by an electrical device. However, Barrett requires that the input voltage be known.
Other methods such as phase control, in which a triac""s conduction angle is ramped up relatively slowly, have proven to yield a universal fusing system which meets IEC 555-3 specifications for flicker yet fails IEC 555-2 specifications for current harmonics. Triac gate phase control also fails conducted power line emission specifications unless excessive additional power filtering is added. In U.S. Pat. No. 4,928,055 to Kaieda et al. (herein referred to as Kaieda) a fuser power control system based on phase delay gated triac control of an AC heating system is taught. While Kaieda was only interested in power control, through proper temperature control algorithm design as taught in co-pending application xe2x80x9cA METHOD FOR REDUCING FLICKER IN ELECTROPHOTOGRAPHIC PRINTERS AND COPIERSxe2x80x9d, Ser No. 08/701,899, their solution could greatly reduces the flicker problem while yielding a universal fuser. However, this solution requires detailed information and the associated expense of voltage magnitude as well as zero cross information for proper triac gate control. This system also suffers from excessive current harmonics as well as places large amounts of conducted emissions on the power grid.
The present invention provides an apparatus for determining an input voltage of a power source. The apparatus has a heating element and a temperature sensor that monitors the temperature of the heating element. A portion of the available power from the power source is applied to the heating element. By measuring a rate of change in the temperature of the heating element the input voltage can be determined.
Once the input voltage has been determined, a temperature control process is used to maintain the temperature of the heating element.